Sockets and Future Functions in Dart - flutter

Question

Summarize the Problem.
I am trying to write an async function that returns data when a receive is completed from a socket. I am having trouble returning the correct data from my async function. The error I am receiving is that the rtn variable is not set and can be null.
Describe what you've tried.
I've tried writing the async function but haven't been getting the desired result. I tried using the late keyword for the variable rtn but that resulted in a runtime exception that the variable was null.
Show some code.
Below, is the function giving me problems. Any advice or resources would be welcomed. I tried going over the Flutter documentation for async but it wasn't too helpful for me.
What I want is that the network data is returned from this async function.
Future<int> fetchNumVideos() async {
int rtn;
Socket.connect(baseStationAddresses[0],
baseStationPort, timeout: const Duration(seconds: 5)).then((socket) =>
{
socket.listen((data) {
String socketData = String.fromCharCodes(data);
print("socketData: $socketData");
rtn = int.parse(socketData);
},
onDone: ((){
socket.destroy();
})
),
}).catchError((onError) {
rtn = 0;
});
return rtn;
}
Thank you!

Answer 1

This issue has been solved by pskink's comment.
The solution was to use the Completer class.
Future<int> fetchNumVideos() async {
final completer = Completer<int>();
Socket.connect(baseStationAddresses[0],
baseStationPort, timeout: const Duration(seconds: 5)).then((socket) =>
{
socket.listen((data) {
String socketData = String.fromCharCodes(data);
print("socketData: $socketData");
completer.complete(int.parse(socketData));
},
onDone: ((){
socket.destroy();
})
),
}).catchError((onError) {
completer.complete(0);
});
return completer.future;
}